When to tell people your pregnant?

I have been told that woman should wait till their 3 months before they tell people "just in case" something were to happen. I can agree that it would be really hard to have to people you had a miss-carriage but how would you be able to keep it in that long? When something happy and exciting happens in your life you want to share it. I have told most of my good friends and a few co workers that I am really close with and of course Joe's parents know and I plan to tell my parents tonight; I don't think thats too much. The fact that I didn't plaster it all over the facebook and sending it to a bunch of people is being conservative about it. I got told from a close co worker of mine today that I should keep it to myself for awhile because I might loose the baby; I know she may be looking out for me but I took it offensivly. It made me sad because as someone who just found out their pregnant doesn't want to hear that. Am I wrong? What are your thoughts?